1. Technical Field of the Invention
This invention relates to radio telecommunication systems and, more particularly, to a system and method for dynamically reallocating channel elements in a loaded code division multiple access (CDMA) radio telecommunications network.
2. Description of Related Art
In radio telecommunications networks, a wide variety of services such as voice, video, data, and image services are available to subscribers. In using these radio telecommunications networks, the most precious resource is the radio spectrum. To maximize the effectiveness of the networks, code division multiple access (CDMA) has been developed to facilitate communications involving a large number of system users. There are other multiple access communication system techniques, such as time division multiple access (TDMA) and frequency division multiple access (FDMA), however, the spread spectrum modulation technique of CDMA has proven to offer many advantages over the other methods.
In a CDMA system, a unique binary spreading sequence, known as a code, is assigned for each call of each user. Multiplied by the assigned code, the user's signal is spread onto a channel bandwidth wider than the user signal bandwidth. The ratio of the system channel bandwidth to the user's bandwidth is known as the "spreading gain." All active users share the same system channel bandwidth frequency spectrum at the same time. The signal of each user is separated from the other users' signals at the receiver by issuing a correlator keyed with the associated code sequence to "de-spread" the desired signal. In this manner, an increased number of simultaneous users can be served.
In addition to serving an increased number of users, the CDMA system uses the technique of macro-diversity to improve the quality of the reception in the radio telecommunications network. The macro-diversity technique involves the use of two or more simultaneous links from two or more cells or base stations to a single mobile station in order to improve the quality or performance of the reception of the radio signal. The mobile station receivers both employ a number of correlators. Receivers using parallel correlators, which are sometimes called rake receivers, allow individual path arrivals to be tracked independently and the sum of their received signal strengths is then used to demodulate the signal. While there is fading on each path arrival, the fading is independent of one another. Demodulation based on the sum of the signals becomes much more reliable using the macro-diversity mode. However, by employing the macro-diversity mode, more resources of the base station are used. In addition, most calls will take place in the macro-diversity mode. Therefore, by the use of the macro-diversity mode, there is a greater likelihood of overloading the radio telecommunications network.
There are disadvantages in the existing system. Although the CDMA system using the macro-diversity mode provides for a clearer reception of radio telecommunication signals, a large amount of resources is used. There may arise a situation where services are needed for additional users, such as emergency calls. At present, there is no method for allowing additional users into the radio telecommunications network when the network has reached full capacity.
Although there are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein, prior art references that discuss subject matter that bears some relation to matters discussed herein are U.S. Pat. No. 5,278,892 to Bollinger et al. (Bollinger), U.S. Pat. No. 5,267,261 to Blakeney, II et al. (Blakeney), and U.S. Pat. No. 5,101,501 to Gilhousen et al. (Gilhousen).
Bollinger discloses a CDMA cellular system comprising a communications network that interconnects cells with each other and with the public telephone network. Bollinger describes a call processing arrangement, in a CDMA network, permitting an interface with the public telephone network. However, Bollinger does not teach or suggest a method or system for accommodating additional users in a CDMA system in a macro-diversity mode.
Blakeney, discloses a CDMA system in which a mobile station user communicates with another system user via at least one base station, where each base station transmits a common pilot signal of a different code phase with respect to other base stations in the system. The mobile station monitors the signal strength of pilot signals and reports the measured signal strength to a system controller via the base station through which it is communicating. Command messages from the system controller to a new base station and the mobile station establish communications through the new base station in addition to the communications through the current base station. When the mobile station detects that the signal strength falls below a predetermined level to at least of one of the base stations through which the mobile station is communicating, the mobile station reports the measured signal strength indicative of the corresponding base station to the system controller via the base station through which it is communicating. Command messages are then sent from the system controller to the identified base station and the mobile station terminates communication through the corresponding base station while communication through the other base station continues. Additionally, Blakeney, describes a mobile station-assisted handoff in a CDMA system. But Blakeney does not teach or suggest a method or system for accommodating additional users in a CDMA system in a macro-diversity mode.
Gilhousen discloses a cellular telephone system for directing communications between a mobile user and cell-sites as a mobile user changes cell-site service areas. Gilhousen describes a method and system for providing a soft handoff in a CDMA cellular telephone system. The system includes circuitry responsive to the indication for coupling communications between the mobile user and the other system user via the new cell-site while the mobile user also remains in communication with the system user via the first cell-site. Gilhousen does not teach or suggest a method or system for accommodating additional users in a CDMA system in the macro-diversity mode.
Thus, it would be a distinct advantage to have a system and method for accommodating these additional users in a radio telecommunications network. It is an object of the present invention to provide such a system and method.